1. Field of the Invention
This invention relates to an image forming assembly, which is used as a component of an image forming apparatus such as an electrostatic (electrophotographic) printer, a photocopier, a facsimile apparatus or the like, and is removably fitted in a housing of the image forming apparatus at a predetermined position along a paper sheet feeding path within the housing and functions as a main portion thereof for forming an image on a paper sheet fed along the paper sheet feeding path, and relates to an image forming apparatus incorporating the same.
More particularly, this invention relates to an image forming assembly, which comprises a first unit including an image carrier and a second unit being independent of the first unit and including image formation relating means such as development means for taking part in an image formation on the image carrier, and an image formation apparatus incorporating the same.
2. Description of the Related Art
FIG. 4 schematically shows an interior construction of an electrophotographic printer as an example of a conventional image forming apparatus of the above described category.
A paper sheet feeding cassette 1 and an image forming assembly 2 are located at their respective predetermined positions in a housing of the above described printer. A paper sheet pick-up roller 3 for picking up a paper sheet one by one from the paper sheet feeding cassette 1 and waiting rollers 4 for forwarding the paper sheet coming from the paper sheet pick-up roller 3 to the image forming assembly 2 with predetermined timing are further mounted in the housing.
The image forming assembly 2 for forming a toner image on the paper sheet coming from the waiting rollers 4 includes a photosensitive drum 5 as an image carrier for carrying an electrostatic latent image, and further includes an electrically charging device 6, a latent image forming head 7, a developing device 8, a transferring device 9 and a cleaner 10, which are arranged around the photosensitive drum 5 in the above mentioned order in a predetermined direction of rotation of the photosensitive drum 5, and all of which are the image formation relating means. While the photosensitive drum 5 makes a full turn in the predetermined direction, the outer peripheral surface of the photosensitive drum 5 is charged with electricity by the electrically charging device 6 and an electrostatic latent image is formed on the electrically charged outer peripheral surface of the photosensitive drum 5 by the latent image forming head 7. Thereafter, the electrostatic latent image on the outer peripheral surface is developed by the developing device 8 to produce a toner image, then, the toner image is transferred by the transferring device 9 onto a paper sheet coming from the waiting rollers 4. Finally, the toner remaining on the outer peripheral surface is removed by the cleaner 10.
In the housing of the conventional printer, fixing rollers 11 for fixing the toner image onto the paper sheet coming from the assembly 2, conveyer rollers 12 for conveying the image carrying paper sheet from the fixing rollers 11 toward a stacking tray 14 disposed outside of the housing and discharging rollers 13 for discharging the image carrying paper sheet coming from the conveyer rollers 12 into the stacking tray 14.
In the housing of the above described conventional printer, a paper sheet feeding path C extends substantially and horizontally from the waiting rollers 4 to the fixing rollers 11, and passes through a narrow space between a lower end of the photosensitive drum 5 and the transfering device 9.
The housing of the conventional printer is constructed by a lower portion M.sub.1 and an upper portion M.sub.2 which is rotatably connected to the lower portion M.sub.1 by means of hinges 15 disposed at one end of the upper portion M.sub.2. In the above described conventional printer, the stacking tray 14, the discharging rollers 13 and the latent image forming head 7 of the image forming assembly 2 are attached to the upper portion M.sub.2 so that they move with the upper portion M.sub.2 as illustrated in FIG. 5.
Relating to the image forming assembly 2, most of the image formation relating means (excepting the latent image forming head 7 which is attached to the upper portion M.sub.2 and the transferring device 9 which is attached to the lower portion M.sub.1) such as the photosensitive drum 5, the electrically charging device 6, the developing device 8, and the cleaner 10 are constructed as one unit or two units. In FIGS. 4 and 5, the photosensitive drum 5, the electrically charging device 6 and the cleaner 10 construct a first unit U.sub.1 provided with a handle 16, and the developing device 8 constructs a second unit U.sub.2 provided with a handle 17.
After the upper portion M.sub.2 is moved to its open position shown in FIG. 5, the one unit or two units can be removed upward from its predetermined position or their predetermined positions in the housing of the conventional printer along an imaginary line crossing the paper sheet feeding path C.
If most of the image formation relating means are constructed as one unit, a paper-jam, happened at a position in the paper sheet feeding path C which is near to the image forming assembly 2, can be readily cleared, because most of the image formation relating means can be removed from the housing of the printer at one time.
In a portable printer, such one unit is removed from the housing of the printer, thrown away and replaced with a new one whenever the photosensitive drum 5 is degraded or the toner in the developing device 8 is used up. Since the toner in the developing device 8 is normally used up before remarkable degradation of the photosensitive drum 5 occurs, the photosensitive drum 5, the electrically charging device 6 and the cleaner 10 all of which are contained in the removed unit are still usable.
Thus, if most of the image formation relating means are constructed as one unit, a running cost of the printer is high. Particularly, since the life of the photosensitive drum 5 has become by far longer than that of the developing device 8 in recent years, the high running cost of the printer is currently very remarkable.
If most of the image formation relating means are constructed as first and second units U.sub.1, U.sub.2 as shown in FIG. 4, only the second unit U.sub.2 containing the developing device 8 can be replaced by a new one when the toner in the developing device 8 is used up, so that the first unit U.sub.1 containing the photosensitive drum 5 can be used much longer until the photosensitive drum 5 is degraded regardless of the using up of the toner in the developing device 8.
In the latter case, however, a paper-jam, happened at a position in the paper sheet feeding path C which is near to the image forming assembly 2, can not be readily cleared because, as illustrated in FIG. 5, the first and second units U.sub.1, U.sub.2 should be separately moved away from the lower portion M.sub.1 with being held separately the respective handles 16, 17 by a hand of an operator after the upper portion M.sub.2 is moved away upward from the lower portion M.sub.1 by rotating the former around the hinges 15 at its one end.